Bristol

iTrader: (1)

Alright. I had some issues with vacuum at idle and the resulting poor braking since my cam swap. I installed a Comp Cams 08-305-8. Ive had 2 different intakes (( Edelbrock TPI and HSR )) and still the same problems. I plugged all the vacuum ports to insure no leaky hoses, used a stetoscope to listen around the plenum and base, tried propane directed at the seams between intake surfaces with a hose. Im fully confident that there are no external leaks. I have had the cam checked and its fine. I made sure that cam/chain is installed properly. I am gonna reseal the rocker shafts tommorrow. I had the intake checked for truness ((warped 0.04")) had it corrected with machine work. ((not the problem as the old intake yielded the same results--> low idle vacuum)). Just to be clear...the vehicle has not been started since the cam and intake have been checked. Im trying to eliminate any possible errors upon my reassembly in order to eliminate all possible sources. Before the cam swap I was using a 08-410-8 with no issues at all. When I originally bought my heads the machine shop set up the valve springs for a 0.550". I am running 1.6 roller rockers. So now with the bigger cam will these springs still be enough? Comp recomends that 986-16 spring set be used. Basically Im asking

1) Could my springs cause vacuum issues?
2) What problems arrise from incorrect springs?
3) What springs should I use?
4) Since most valve springs appear to be reccomended for cam specs based on a 1.5 rocker...is there a formula the calculates the total lift of a cam with different rocker ratios?

I appologize if this post is naive or a "repeat" but Im getting pretty frustrated and Im sure Im over looking something. Any advice etc. is really appreciated.

Thanks
Kris

ME Leigh

Not likely that your springs will cause vaccum problems but its probably your cam choice, what is it? Your cam choice will ultimately effect your vaccum.

ede

you can "set up" springs for any random lift. did they shim or oter wise rig your original springs? you need springs to match the cam. the formula to figure total lift is the ratio and the cam lift

Bristol

iTrader: (1)

Before you guys get all over me...I know I should have got the matching springs....the heads were Edelbrock Performers and they shimmed the Edelbrock springs to apparently 0.550" and with my calculations the max lift is 0.544". The cam is a Comp Cams 08-305-8 and according to Comp Cams this cam should produce 15". I was just curious what you all thought on the spring issue as to possibly causes and what reccomendations you guys had. Thanks

Kris